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IEEE Spectrum has a story on research into graphene which shows protons can pass through the material. One of the key properties of graphene was that it was previously thought to be impermeable to gases and liquids:
But as Geim and his colleagues discovered, in research that was published in the journal Nature, monolayers of graphene and boron nitride are highly permeable to thermal protons under ambient conditions. So hydrogen atoms stripped of their electrons could pass right through the one-atom-thick materials.
This has significant applications in fuel cells, since proton exchange membrane fuel cells require a barrier that only passes protons, and this discovery could be used to improve the efficiency of existing designs. However in addition to this it could also allow the cells to extract hydrogen directly from humid air
It is conceivable, based on this research, that hydrogen production could be combined with the fuel cell itself to make what would amount to a mobile electric generator fueled simply by hydrogen present in air.
“When you know how it should work, it is a very simple setup,” said Marcelo Lozada-Hidalgo, a PhD student and corresponding author of this paper, in a press release. “You put a hydrogen-containing gas on one side, apply a small electric current, and collect pure hydrogen on the other side. This hydrogen can then be burned in a fuel cell.”
Additional detail is available at Science Daily and in the original press release from the University of Manchester.
(Score: 2) by Zinho on Thursday December 04 2014, @07:41PM
my understanding is that motors aren't all that efficient. Neither are chemical batteries. Burning hydrogen is relatively efficient. But producing hydrogen is terribly inefficient thus for now making the all-electric advocates correct.
You're thinking along the right lines, you just need one more idea to close the circle and line up with the "no perpetual motion" crowd:
That's why the Thermo geeks are always saying "just use the battery". Even if the intermediary steps are super efficient, any system that goes Battery->Losses->Electricity would be better built as Battery->Electricity. Unless you're getting energy input from somewhere other than the battery (collecting free H2 from the air would work, assuming that there's enough) this will always be a valid argument.
The real question is whether the H2 generator they want to run off of the battery produces more energy value in H2 than the battery's own capacity. If they're using hydrolysis then the answer is no. Collecting atmospheric hydrogen is a possibility, and I wish them luck at overcoming the engineering challenges. Concentrating the H+ from the parts-per-million level to useful volumes and pressures isn't trivial.
To answer your last question, yes, we have an idea of when we'll know we've hit peak efficiency. Carnot's Theorem (derived in the 1820s and reinforced by refined theory, experimentation, and engineering practice ever since) is one of our most useful yardsticks in this field. I'd like to warn you before you start reading about it that it gives depressing answers. For example, a perfectly efficient heat engine operating between 0 and 100 degrees Celsius will have a maximum efficiency of 27%. The reasons for this are well understood in the Engineering and Physics disciplines, and easy to explain to anyone willing to sit and think about them. There are several good tutorials on the web [virginia.edu], and your local library may have textbooks on the subject you can check out (your local University library certainly will, even if you have to read it on-site). Generally, you know to stop looking for a better answer when the one you have is close enough to ideal and doing better starts to cost too much.
Please pardon the Thermo geeks when they turn jaded, skeptical eyes on a new proposal and ask "where is the extra energy coming from". You can only explain a certain number of times that a heat engine won't run between reservoirs at the same temperature, after a while you get tired and refuse to talk to anyone who brings up ZPE and the like.
Of course, that doesn't stop us from looking for better systems. The answer to "how can I make my system better" is often "replace it with a better system" :P Novel sources of energy are always welcome, provided that there is actually energy to extract there.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by morgauxo on Tuesday December 09 2014, @05:26PM
Thanks, your answer is very informative, I'll be looking up Carnot's Theorem.
I do have one question though... why does the purpose of the fuel cell HAVE to be to produce electricity?
I'll admit I'm not necessarily speaking to the article, more just thoughts about ways to power a car. I was thinking the hydrogen would be burnt in an internal combustion engine. It would be another way to consume electricity to produce motion, rather than a way to produce electricity. I was pitting the efficiency of electrolysis plus an internal combustion engine against the efficiency of an electric motor.
I know electric motors and internal combustion engines have been studied and optimized for ages now. My understanding is that Electrolysis is a weak link, very inefficient but recently a lot of research has been put into it with some promissing results using nano-materials. Is it possible that electrolysis plus internal combustion could one day beat electric motor? It sounds unlikely to me but I know that I do not have the physics background to answer that for sure and I am curious.
I do know that either way the energy source is likely a battery which gets charged from the grid at night and nothing free and magical.
(Score: 2) by Zinho on Friday December 12 2014, @06:28PM
... why does the purpose of the fuel cell HAVE to be to produce electricity?
The answer to this question is easy; that's what fuel cells [wikipedia.org] do. If it doesn't take in fuel and oxidizer and produce water + electricity then it's not a fuel cell.
I was pitting the efficiency of electrolysis plus an internal combustion engine against the efficiency of an electric motor
OK, that's reasonable. Bear with me for a bit.
The first big obstacle you'll run into is the very high efficiency of electric motors: good ones run up to 94% under the right conditions, and degrade to about 78% under poor conditions [1]. These are practical efficiency measurements, not theoretical; electric motors are really that good.
In contrast, an internal combustion engine (I.C.E.) running the Carnot cycle (impossible) with H2 and ambient air [wikipedia.org] as fuel/oxidizer will run at a theoretical maximum of ~91%; real engines use the Otto cycle [wikipedia.org] which is limited by the autoignition temperature [wikipedia.org] of the fuel, which puts a ceiling on compression ratio.[2] Gasoline engines are limited to about 60% efficiency due to this; a back-of-the-envelope calc based on H2 autoignition suggests we could increase compression by half[3] and boost ideal H2 Otto efficiency to 66%. These are again theoretical maximum values, in practice they will be lower (55% or less would not surprise me).
That gap between 90% and 66% is a lot to make up for. To beat the efficiency of running a motor off of the battery you would literally need to extract 36% more energy potential in H2 + O2 during your electrolysis stage than you spent on electricity to operate the separator (0.9 = 1.36 * 0.66); this is a definitive example of an "over unity" device [4]. You're not going to get efficiency greater than 1 on any process without extracting more energy from somewhere, even with an efficient catalyst (as pointed out to me in another part [soylentnews.org] of this thread). So no, regardless of how efficiently you perform electrolysis it will never catch up to just running an electric motor off of the battery.
Thermodynamics is a harsh mistress.
[1] source [energy.gov], PDF warning, see attachment C on page 13
[2] if you want to do your own math on this, remember that you need to convert to Absolute temperature scales; add 273.15 degrees to Celsius to get Kelvin. Any math for Thermodynamics that asks for temperature assumes you're on a temperature scale that starts at absolute zero instead of some phase transition of water.
[3] I used the Ideal Gas Law [wikipedia.org] as my base for this calculation, which makes assumptions about temperatures and pressures being around 20 C and 1 Atm. Given the high temperatures and pressures typical of the Otto cycle those assumptions may break down making my estimate incorrect, but it's probably close.
[4] Beating this dead horse some more: basically to make electrolysis even an option, you'd need to start with an I.C.E. more efficient than an electric motor. Carnot's theorem says you're going to fall short there when using Hydrogen, regardless of how good your engine is.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin